If a switch receives a superior BPDU and goes directly into a blocked state, what mechanism
must be in use?
A.
BPDU guard
B.
portfast
C.
EherCahannel guard
D.
loop guard
Explanation:
The key here is the word ‘switch’. The entire switch goes into a blocked state, meaning that it
can’t participate in STP, it is blocked. Root guard basically puts the port in a listening state
rather than forwarding, still allowing the device to participate in STP.
This same question is asked with rootguard as one of the options. BPDU guard would put a port into errdisable state
“PortFast BPDU guard prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port. When you enable BPDU guard on the switch, spanning tree shuts down PortFast-configured interfaces that receive BPDUs instead of putting them into the spanning tree blocking state.May 6, 2007”
The explanation about root guard is correct also however, in that only the port is put into the root-inconsistent state rather than blocking. Neither answer has the “switch” put into a blocking state, but “superior BPDU” implies that some BPDU was accepted. BPDU guard would not accept any BPDU, because hosts on a port with portfast enabled have no business issuing any.
Root guard